SMD LED 19-21 Dark Red Datasheet - Dimensions 2.0x1.25x0.8mm - Voltage 1.75-2.35V - Power 60mW - English Technical Documentation

1. Product Overview

This document details the specifications for a surface-mount device (SMD) LED in the 19-21 package size, emitting a dark red color. This component is designed for modern electronic assembly processes, offering a compact footprint and reliable performance for various indicator and backlighting applications.

1.1 Core Advantages and Product Positioning

The primary advantage of this 19-21 SMD LED is its significantly reduced size compared to traditional lead-frame type LEDs. This miniaturization enables several key benefits for product designers:

• Smaller Board Size: Allows for more compact PCB designs.
• Higher Packing Density: More components can be placed in a given area.
• Reduced Storage Space: Smaller components require less inventory space.
• Lightweight Construction: Ideal for portable and miniature applications where weight is a critical factor.
• Compatibility: The device is packaged on 8mm tape on a 7-inch diameter reel, making it fully compatible with standard automatic pick-and-place equipment used in high-volume manufacturing.

The product is positioned as a general-purpose indicator and backlight solution, particularly suited for applications where space and weight are at a premium.

1.2 Target Market and Applications

This LED is designed for a broad range of electronic applications. Its key target markets include:

• Automotive Interior: Backlighting for dashboard instruments, switches, and control panels.
• Telecommunications: Status indicators and keypad backlighting in telephones, fax machines, and other communication devices.
• Consumer Electronics: Flat backlighting for LCD displays, symbol illumination, and switch backlighting.
• General Indicator Use: Any application requiring a reliable, compact red status or indicator light.

2. Technical Specifications Deep Dive

This section provides a detailed, objective analysis of the LED's technical parameters. Understanding these limits is crucial for reliable circuit design.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed and should be avoided for long-term reliability.

• Reverse Voltage (V_R): 5V. Exceeding this voltage in reverse bias can cause immediate junction breakdown.
• Continuous Forward Current (I_F): 25mA. The maximum DC current for continuous operation.
• Peak Forward Current (I_FP): 60mA (Duty Cycle 1/10 @ 1kHz). This rating is for pulsed operation only and must not be exceeded even momentarily in DC operation.
• Power Dissipation (P_d): 60mW. The maximum power the package can dissipate as heat, calculated as V_F * I_F.
• Electrostatic Discharge (ESD) Human Body Model (HBM): 2000V. Provides a measure of the device's sensitivity to static electricity. Proper ESD handling procedures are mandatory.
• Operating Temperature (T_opr): -40°C to +85°C. The ambient temperature range over which the device is specified to operate.
• Storage Temperature (T_stg): -40°C to +90°C.
• Soldering Temperature:
  • Reflow Soldering: 260°C peak for a maximum of 10 seconds.
  • Hand Soldering: 350°C at the iron tip for a maximum of 3 seconds per terminal.

2.2 Electro-Optical Characteristics (Ta=25°C)

These are the typical performance parameters measured under standard test conditions (25°C ambient, I_F=5mA).

• Luminous Intensity (I_v): 7.2 mcd (Min) to 18.0 mcd (Max). The actual output is binned (see Section 3).
• Viewing Angle (2θ_1/2): 100 degrees (Typical). This is the full angle at which the luminous intensity drops to half of its peak value.
• Peak Wavelength (λ_p): 639 nm (Typical). The wavelength at which the spectral emission is strongest.
• Dominant Wavelength (λ_d): 625.5 nm (Min) to 637.5 nm (Max). This is the single wavelength perceived by the human eye, defining the color. It is also binned.
• Spectral Bandwidth (Δλ): 20 nm (Typical). The width of the emission spectrum at half the maximum intensity.
• Forward Voltage (V_F): 1.75V (Min) to 2.35V (Max) at I_F=5mA. This parameter has a tight tolerance of ±0.1V and is binned.
• Reverse Current (I_R): 10 μA (Max) at V_R=5V. It is critical to note that the device is not designed for operation in reverse bias; this test is for leakage characterization only.

3. Binning System Explanation

To ensure consistent color and brightness in production, LEDs are sorted into bins based on key parameters. This allows designers to select parts that meet specific application requirements.

3.1 Luminous Intensity Binning

LEDs are categorized into four bins (K1, K2, L1, L2) based on their light output at 5mA.

• K1: 7.2 - 9.0 mcd
• K2: 9.0 - 11.5 mcd
• L1: 11.5 - 14.5 mcd
• L2: 14.5 - 18.0 mcd

A tolerance of ±11% applies within each bin.

3.2 Dominant Wavelength Binning

The color (hue) is controlled by binning the dominant wavelength into three ranges (E6, E7, E8).

• E6: 625.5 - 629.5 nm
• E7: 629.5 - 633.5 nm
• E8: 633.5 - 637.5 nm

A tolerance of ±1nm applies within each bin.

3.3 Forward Voltage Binning

To aid in current regulation design, especially in parallel strings, forward voltage is binned.

• Bin 0: 1.75 - 1.95 V
• Bin 1: 1.95 - 2.15 V
• Bin 2: 2.15 - 2.35 V

A tolerance of ±0.1V applies within each bin.

4. Performance Curve Analysis

The datasheet provides several characteristic curves that are essential for understanding the LED's behavior under non-standard conditions.

4.1 Luminous Intensity vs. Ambient Temperature

This curve shows that luminous intensity decreases as ambient temperature increases. This is a fundamental characteristic of semiconductor light sources due to reduced internal quantum efficiency at higher temperatures. Designers must derate the expected light output if the LED will operate in a high-temperature environment.

4.2 Luminous Intensity vs. Forward Current

The relationship between current (I_F) and light output is generally linear at lower currents but can become sub-linear at higher currents due to heating and efficiency droop. Operating above the recommended current will not yield proportional increases in brightness and will reduce lifespan.

4.3 Forward Current vs. Forward Voltage (I-V Curve)

This is the fundamental diode characteristic. The curve shows an exponential relationship. A small change in voltage results in a large change in current, highlighting the critical need for current-limiting circuitry (e.g., a series resistor or constant current driver) to prevent thermal runaway and destruction.

4.4 Forward Current Derating Curve

This graph defines the maximum allowable continuous forward current as a function of ambient temperature. As temperature rises, the maximum safe current must be reduced to stay within the device's power dissipation limits and prevent overheating.

4.5 Spectrum Distribution

The spectral plot confirms the monochromatic nature of this AlGaInP-based LED, showing a narrow emission peak centered around 639 nm, which corresponds to a deep red color. The 20nm bandwidth indicates the spectral purity.

4.6 Radiation Pattern

The polar diagram illustrates the 100-degree viewing angle. The intensity is highest at 0 degrees (perpendicular to the LED face) and decreases symmetrically towards the edges, following a near-Lambertian pattern typical for this package style.

5. Mechanical and Package Information

5.1 Package Dimensions

The 19-21 SMD LED has the following key dimensions (tolerance ±0.1mm unless specified):

• Length: 2.0 mm
• Width: 1.25 mm
• Height: 0.8 mm

A cathode mark is clearly indicated on the package for correct polarity orientation during assembly.

5.2 Pad Design and Polarity

The recommended footprint (land pattern) is provided in the dimension drawing. Correct identification of the cathode (typically marked by a green tint, a notch, or a beveled corner as shown) is essential to prevent reverse connection during soldering.

6. Soldering and Assembly Guidelines

Adherence to these guidelines is critical for ensuring solder joint reliability and preventing damage to the LED.

6.1 Reflow Soldering Profile (Pb-free)

The recommended temperature profile is crucial for Pb-free (SAC) solder alloys:

• Pre-heating: 150-200°C for 60-120 seconds. This gradually heats the board to minimize thermal shock.
• Time Above Liquidus (217°C): 60-150 seconds.
• Peak Temperature: 260°C maximum.
• Time Within 5°C of Peak: 10 seconds maximum.
• Maximum Ramp-Up Rate: 6°C/second.
• Maximum Ramp-Down Rate: 3°C/second.
• Reflow Limit: The device should not undergo reflow soldering more than two times.

6.2 Hand Soldering Precautions

If hand soldering is necessary, extreme care must be taken:

• Use a temperature-controlled iron set to a maximum of 350°C.
• Limit contact time to 3 seconds per terminal.
• Use an iron with a power rating of 25W or less.
• Allow a minimum 2-second cooling interval between soldering each terminal.
• Avoid applying mechanical stress to the LED body during heating.

6.3 Rework and Repair

Repair after soldering is strongly discouraged. If absolutely unavoidable, a specialized double-head soldering iron must be used to simultaneously heat both terminals, allowing the component to be lifted without twisting. The potential for damage is high, and the characteristics of the LED should be verified after any rework.

7. Storage and Moisture Sensitivity

This component is moisture-sensitive. Improper handling can lead to \"popcorning\" (package cracking) during reflow due to rapid vapor expansion.

7.1 Storage Conditions

• Do not open the moisture-proof barrier bag until the components are ready for use.
• After opening: Store at ≤30°C and ≤60% Relative Humidity (RH).
• Floor Life: Use within 168 hours (7 days) of opening the bag.
• If not used within this time, reseal with desiccant or rebake.

7.2 Baking Instructions

If the desiccant indicator has changed color or the floor life has been exceeded, bake the components before use to remove absorbed moisture.

• Temperature: 60°C ±5°C
• Duration: 24 hours
• Note: Ensure the baking temperature does not exceed the maximum storage temperature (90°C).

8. Packaging and Ordering Information

8.1 Packaging Specifications

• Carrier Tape: 8mm width.
• Reel Size: 7-inch diameter.
• Quantity per Reel: 3000 pieces.
• Packaging: Components are sealed in an aluminum moisture-proof bag with desiccant and a humidity indicator card.

8.2 Label Explanation

The reel label contains critical information for traceability and identification:

• CPN: Customer's Part Number (if assigned).
• P/N: Manufacturer's Part Number (e.g., 19-21/R7C-AK1L2BY/3T).
• QTY: Packing quantity on the reel.
• CAT: Luminous Intensity bin code (e.g., K1, L2).
• HUE: Dominant Wavelength/Chromaticity bin code (e.g., E6, E7).
• REF: Forward Voltage bin code (e.g., 0, 1, 2).
• LOT No: Manufacturing lot number for traceability.

9. Application Design Considerations

9.1 Current Limiting is Mandatory

This is the single most important design rule. The LED must be driven with a constant current or have a series resistor calculated based on the supply voltage (V_supply), the LED's forward voltage (V_F from its bin), and the desired current (I_F ≤ 25mA). The formula for the resistor is: R = (V_supply - V_F) / I_F. Without this, a small increase in supply voltage will cause a large, potentially destructive increase in current.

9.2 Thermal Management

While the package is small, power dissipation (up to 60mW) generates heat. Ensure adequate PCB copper area (thermal relief pads) around the solder pads to help dissipate heat, especially if operating near maximum current or in high ambient temperatures. Refer to the derating curve.

9.3 ESD Protection

With an ESD HBM rating of 2000V, this device has moderate sensitivity. Implement ESD protection on input lines if they are exposed to user contact, and always follow standard ESD-safe handling procedures during assembly and prototyping.

10. Technical Comparison and Differentiation

The 19-21 package offers a specific balance of size and performance.

• vs. Larger SMD LEDs (e.g., 3528): The 19-21 is significantly smaller, saving board space, but typically has lower maximum current and light output ratings.
• vs. Smaller SMD LEDs (e.g., 0402): The 19-21 is easier to handle and solder manually, offers higher power handling, and often has a wider viewing angle.
• vs. Through-Hole LEDs: The SMD format eliminates the need for drilled holes, enables automated assembly, reduces weight, and allows for much higher component density on the PCB.
• AlGaInP Technology: This material system is known for high efficiency in the red/orange/amber color range, offering good brightness and color stability compared to older technologies.

11. Frequently Asked Questions (FAQ)

11.1 Can I drive this LED directly from a 3.3V or 5V supply?

No. You must use a series current-limiting resistor. For example, with a 5V supply and an LED with a V_F of 2.0V at 20mA: R = (5V - 2.0V) / 0.020A = 150 Ω. A 150Ω resistor is required.

11.2 Why is the luminous intensity specified at 5mA instead of the maximum 25mA?

5mA is a standard test condition that allows for consistent comparison between different LED models and bins. You can operate it at higher currents (up to 25mA) for higher brightness, but you must refer to the \"Luminous Intensity vs. Forward Current\" curve and ensure thermal limits are not exceeded.

11.3 What do the bin codes (e.g., K1, E7, 1) mean for my design?

If your application requires consistent brightness across multiple LEDs, you should specify a tight luminous intensity bin (e.g., only L1). If color consistency is critical, specify a tight wavelength bin (e.g., only E7). For designs where LEDs are connected in parallel, specifying a tight forward voltage bin (e.g., only 1) helps ensure current sharing is more even.

11.4 The datasheet says \"not designed for reverse operation.\" What does this mean?

It means the LED should never be intentionally operated with the cathode at a higher voltage than the anode. The 5V reverse voltage rating is a maximum survivable rating for accidental transient events, not an operating condition. Permanent damage is likely if reverse voltage is applied during normal operation.

12. Design and Usage Case Study

Scenario: Designing a compact automotive switch with red backlighting.

1. Component Selection: The 19-21 Dark Red LED is chosen for its small size, suitable brightness, and compatibility with automated assembly.
2. Circuit Design: The vehicle's 12V system is used. A series resistor is calculated. Assuming a forward voltage bin of 2.0V and a desired current of 15mA for adequate brightness and long life: R = (12V - 2.0V) / 0.015A ≈ 667 Ω. A standard 680 Ω, 1/8W resistor is selected.
3. PCB Layout: The compact 19-21 footprint is placed under the switch dome. A small amount of extra copper is added to the solder pads for heat dissipation.
4. Manufacturing: LEDs from bin L1 (for consistent brightness) and E7 (for consistent color) are ordered on 7-inch reels for automated pick-and-place.
5. Assembly: The sealed reel is used within its 7-day floor life. The PCB undergoes a single reflow pass using the specified Pb-free profile.
6. Result: A reliable, uniformly lit switch backlight with a long operational lifespan.

13. Technology Principle Introduction

This LED is based on AlGaInP (Aluminum Gallium Indium Phosphide) semiconductor material grown on a substrate. When a forward voltage is applied across the p-n junction, electrons and holes are injected into the active region where they recombine. In a direct-bandgap semiconductor like AlGaInP, this recombination releases energy primarily in the form of photons (light). The specific ratio of aluminum, gallium, and indium in the crystal lattice determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, deep red (~639 nm). The water-clear resin lens encapsulates the chip and shapes the emitted light into the specified 100-degree viewing angle.

LED Specification Terminology

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